How Diabetes Causes Blindness

Topic Contents

How Diabetes Causes Blindness

Topic Overview

Over time, high blood sugar levels from diabetes lead to
damage of the retina, the layer on the back of the eye that captures images and
sends them as nerve signals to the brain. Whether diabetic retinopathy develops
depends in part on how high blood sugar levels have been and how long they have
been above a target range. Other things that may increase your risk for
diabetic retinopathy include high blood pressure, pregnancy, a family history
of the condition, kidney disease, high cholesterol, and whether you
smoke.

Early retinopathy

The early stages of retinal damage
are called nonproliferative retinopathy. First, tiny blood vessels called
capillaries in the retina develop weakened areas in their walls called
microaneurysms. When red blood cells escape through these weakened walls, tiny
amounts of bleeding (hemorrhages) become visible when the retina is viewed
through an instrument called an ophthalmoscope. To clearly see your retina, the
ophthalmologist will enlarge (dilate) your pupils (which serve as a window to
the back of your eye) and may also use a special dye to help identify blood
vessels that may be leaking.

Fluid from the blood also escapes,
leading to yellowish "hard exudates." This type of damage does not cause
problems with vision unless some of the leaking fluid is near the macula. (The macula
is the area of the retina that is responsible for central vision.) An
ophthalmologist who specializes in the treatment of retinal problems will
attempt to stop blood leakage by using a laser in a process called
photocoagulation. By using an appropriately selected laser, your
ophthalmologist may seal the small blood vessels that can leak when a person
has nonproliferative and proliferative retinopathy. More recently, ophthalmologists have been using injectable medicines to treat retinal leakage.

If fluid
leaks out near the macula, it can disrupt vision. This is called macular edema.
As retinopathy becomes more severe, parts of the abnormal capillaries can
become closed off. This kills parts of the retina that the capillaries previously
supplied with blood. These tiny damaged parts of the retina are called "cotton
wool" spots and can be seen using an ophthalmoscope.

Late retinopathy

The later stages of retinal injury
are called proliferative retinopathy, because new fragile blood vessels grow to
supply the damaged areas of the retina. These new blood vessels can bleed into
the
vitreous gel, the gel-filled area in front of the
retina. Over time, scar tissue that forms from bleeding can cause the retina to
detach from the wall of the eye (retinal detachment) and cause loss of vision.

Severe proliferative retinopathy may be treated with laser
surgery in order to save vision. Your eye doctor may use more aggressive laser
therapy, called scatter (pan-retinal) photocoagulation. This process is more
thorough than that used in localized photocoagulation. And it may require more
individual treatments. But it allows your doctor to minimize the growth of new
blood vessels across the back of your retina. Severe proliferative retinopathy
may also be treated with medicines that slow the growth of abnormal blood
vessels in the retina. The growth of these vessels is triggered by a protein
called vascular endothelial growth factor (VEGF).
Anti-VEGF medicines , such as ranibizumab (Lucentis), block the
effects of VEGF.

Laser treatments may not always work in treating proliferative
retinopathy. If you have retinal detachment or hemorrhages that cannot be
repaired, your retinal specialist will need to use a surgical technique to
try to restore your vision. This surgical technique, called pars plana
vitrectomy, attempts to repair your retina and reduce hemorrhaging. Like many
surgical techniques, it has several risks and is much
more likely to damage your eye than laser surgery.

Other eye problems

People who have diabetes are also at
risk for other problems, such as
cataracts and
glaucoma, that damage vision. They are also at risk for a severe form of glaucoma called
neovascular glaucoma. Cataracts are frequently caused
by a lifetime of sun exposure, and diabetes speeds up their
formation.

The following table outlines the major causes of
blindness in people who have diabetes.

Causes of blindness and how to prevent it

Condition

How it causes vision loss

Preventive measures

Diabetic retinopathy

Damages the retina, the section of your eye
responsible for capturing visual information

Controlling hemoglobin A1c
levels

Controlling blood pressure

Having regular eye
exams

Using laser surgery early to treat retinopathy

Glaucoma

Increases pressure in the eye, which results in
damage to your retina

Having regular eye exams to check for the
disease

Cataracts

Cloud the lens, the section of your eye responsible
for focusing light on your retina

If you notice problems with your vision, you should
immediately seek medical evaluation by an ophthalmologist. Regular eye exams
are meant to detect any retinopathy at the nonproliferative stage, where it may
still be treated with a good chance of success.

If
nonproliferative retinopathy is not detected and treated early, it may progress
to proliferative retinopathy. During proliferative retinopathy, your body
tries to correct the microaneurysms. To replace blood vessels that have
broken or leaked, new blood vessels begin to form. These blood vessels are
fragile and may break easily, causing bleeding into the middle of the eye and
clouding vision. They also form scar tissue that can pull on the retina and
cause the retina to detach from the wall of the eye.

With
aggressive management of your condition—keeping hemoglobin A1c levels below 7%
and controlling blood pressure—along with regular screening of your vision, you
may be able to prevent or delay blindness.

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